off-the-record
dark
crypto-
mum
secretomal
secernent
occulted
closehanded
top secret
under wraps
subterranean
on the down-low
under the covers
pseudosecret
make known
spill the beans
supersecret
secretomics
on the hush
latently
exposure
secret of Polichinelle
closehandedness
something nasty in the woodshed
ultrasecret
hidness
divulgation
underwrapped
concealment
confidence
ectocrine
incretion
darkness
keep a lid on
in petto
cryptadia
out
occult
underhand
clandescent
secret
secretive
nonsecret
concealing
underhanded
hiding
tip one's hand
backstage
covert
let the cat out of the bag